Clos and Fat-Tree network topologies have gained prominence in today's networks (especially in today's data-center networks). A typical clos network may be a highly-connected multistage network in which nodes at each stage are connected to all nodes in each prior and/or subsequent stages. For example, a typical three-stage clos network may include three stages of nodes in which the nodes in the middle stage are connected to all nodes in the ingress and egress stages of the network. A typical fat-tree network may be considered a special folded form of a clos network that is configured using a leaf-spine topology. In a typical fat-tree network, each leaf node in the network (i.e., each node at the lowest level in the network) may be connected to each spine node in the network (i.e., each node at the highest level in the network). For example, a typical three-level fat-tree network may include two or more branches (or Points of Delivery (PoDs)) that each have a clos-network topology. In each branch of the three-level fat-tree network, each leaf node may be connected to each middle-level node in the branch, and each middle-level node may be connected to each spine in the network.
Unfortunately, existing underlay routing protocols (e.g., the Open Shortest Path First (OSPF) routing protocol, the Intermediate System to Intermediate System (IS-IS) routing protocol, the Enhanced Interior Gateway Routing Protocol (EIGRP), and the Border Gateway Protocol (BGP)) have typically been geared towards networks with irregular topologies and low degrees of connectivity as compared to typical clos networks. The lack of underlay routing solutions that natively address highly-connected clos networks has led many data-center operators to create alternative routing-protocol solutions by haphazardly modifying existing protocols, with mixed results overall. The instant disclosure, therefore, identifies and addresses a need for systems and methods for distributing routing-protocol information in clos fabrics.